A need often arises to interconnect telephone communications with mobile radio systems. This is especially true for public service RF communications systems. There are numerous occasions when a police officer, fireman, taxi driver or other mobile radio user needs to place or receive a telephone call. For example, a police officer might telephone an informant to obtain information for a search warrant or before entering a crime scene. Similarly, a crime victim may call the police officer on patrol whom the victim previously talked to about a crime. A paramedic might telephone the parents of a child in an accident to obtain the child's medical history. Accordingly, it would facilitate these communications if the mobile radio user could place or receive telephone calls through the mobile radio.
Interconnecting radio and telephone systems :has been complicated and expensive in the past. Previously, telephone connections with an RF system were placed manually through a central dispatcher or a mobile radio operator. Requiring a live operator to set up a telephone call is both expensive and time consuming. More modern RF systems have telephone interconnect hardware at individual site controllers and base stations. One example of a site based telephone connection is the EDACS.TM. telephone interconnect system offered by the assignee of this invention.
This type of site based hardware is suitable for single site RF systems, but does not work well for multisite systems for several reasons. First, expensive electronic hardware is required at each site controller. A user cannot place a telephone call when he is within a site for which the controller lacks telephone connection hardware. Second, an incoming telephone call must be placed to the particular site having the callee. If the caller does not know the site in a multisite system that has the intended callee, then the caller cannot place the call. Third, a mobile radio callee or caller cannot move out of a site handling an ongoing telephone call without terminating the call. There are other disadvantages of having telephone connection hardware located at one or more individual site controllers without centralized control over telephone communications.
The present invention relates to an apparatus and method for connecting telephone lines to a multisite distribution switch for a network of several single site trunked radio systems. An example of a single site transceiver system is disclosed in commonly-assigned U.S. Pat. No. 4,905,302, entitled "Trunked Radio Repeater System" and U.S. Pat. No. 4,903,321 entitled "Radio Trunking Fault Detection System" which are incorporated by reference. Digital trunked radio transceivers capable of handling communications between numerous mobile units and dispatcher consoles in a single area are known.
Multiple transmitting sites are necessary to provide RF communications to all locations within many cities, towns, counties or other localities. For example, multiple transmitters may be needed to cover a rural community covering many square miles or a city having many buildings. FIG. 1 is a schematic diagram of a simplified multiple-site system having three radio repeater (transmitting) central sites S1, S2, and S3 providing communications to geographic areas A1, A2, and A3, respectively. Mobile or portable transceivers within area A1 receive signals transmitted by site S1, transceivers within area A2 receive signals transmitted by site S2, and transceivers within area A3 receive signals transmitted by site S3. Each site has a site controller that acts as a central point for communications in the site. To enable communications from one area to another, a switch connects the radio systems together as a united network to establish audio slots connecting one site controller to another. The caller and callee communicate through their respective interconnected site controllers. A mobile radio caller in one area can communicate with another mobile use in another site area.
In the present invention a telephone call may be made from or to a mobile radio any where in a multisite RF trunked repeater system. The multisite switch connects with a telephone system through a centralized telephone interconnect system (CTIS). Since the multisite switch links together a network of mobile radio systems a radio user in one area (e.g. A1) can communicate with a callee in another area (e.g. A2) or place a telephone call (e.g. T1) through the multisite switch. In addition, a telephone call can be grouped with other radio calls so that more than one radio user can participate in the telephone call. Moreover, existing telephone interconnect hardware at an individual site, e.g., S.sub.3, can be used in conjunction with the telephone handling capacity of the CTIS at the multisite switch.
In multisite, the site controller (S1) receives a call from a mobile radio in A1 requesting a channel to communicate with a specific callee. A caller requests a channel simply by pressing the push-to-talk (PTT) button on his microphone. This informs the site controller that a channel is requested. The PTT signal is transmitted to the unit on a control channel that is continuously monitored by the site controller. The site controller assigns a channel to the call and instructs the caller's radio unit to switch from the control channel to the channel assigned to the call. This assigned channel is applicable only within the area covered by the site.
If the mobile unit is placing a telephone call, it sends a channel request for a telephone line to the site controller. The site controller will assign a working channel to the call and command the mobile radio to switch to the assigned working channel. In addition, the site controller will connect the assigned channel to a telephone line (T.sub.1) if the controller has on a site telephone line connection.
To connect a call from one site to another site or to a centralized telephone connection, the site controller sends the channel assignment to the multisite network switch. The switch activates an internal audio slot for the call. The switch also sends a channel request to all CTIS and other site controllers or to only those site controllers having a designated callee within their site area. If a telephone connection is required, the telephone interconnect node (CTIS) of the multisite switch responds to the channel request message from the originating node by assigning a telephone line to the call and coupling the assigned line to the internal switch audio slot assigned to the call The call is transmitted to the originating site controller, routed through the assigned audio slot in the switch and retransmitted by the secondary sites on various assigned channels in those other areas and/or coupled into a telephone communication. For telephone calls, a second path is established from the telephone connection at the switch through a second audio slot in the switch, to the site controller and to the mobile user via the previously assigned site working channel.
When the caller ends the call, the originating site controller deactivates the assigned channel for that site and notifies the network switch that the call is terminated. There may be a brief "hang time" after the end of the call during which the channel remains assigned. During this hang time, the call can be rekeyed without going through the channel assignment procedure.
When the call is dropped, the telephone connection is broken. Similarly, the network switch sends an end of call command to the secondary site controllers. A call is terminated in a similar format and operation as the slot assignment. Instead of establishing an audio route between sites and through the switch, the drop call command causes the assigned channels to be released.
In addition to providing communications between mobile radio units in different areas, the multisite network switch provides communications between dispatchers and mobile radio units. The dispatcher consoles are connected to the network switch in the same manner as are the site controllers. A dispatcher console can issue a channel call request through the network switch to a site controller in another area to call a mobile unit or to another dispatcher console to call a dispatcher in another area.
In addition to all of the features that the mobile units have, each dispatcher console has the ability to participate in any call, including telephone calls, in its area or to its assigned groups. Thus, when a call comes through the network switch from another area or a telephone line to a mobile radio, the network switch informs the dispatcher console of the call in addition to notifying the site controller. The dispatcher can listen in or participate in the call.
The network switch is also capable of handling calls to groups of mobile units and/or dispatcher consoles. The wide area switch manages group calls and monitors the network to ensure that the site controllers for all of the callees in the group assign a channel to the group call. If a channel is not assigned, the wide area switch advises the caller that the wide area call cannot be formed as requested. The caller then has the option of re-keying the call so as to reach those areas having assigned channels.
The multisite switch maintains site and track masks in its databases to identify and locate the site having each unit and group in the entire radio system covered by the multisite switch. Thus, a telephone caller need only know the telephone number for the multisite switch and an identifier number for the callee's mobile radio unit. The multisite switch then routes the telephone call to the particular site having the callee.
A database site mask is maintained for each radio unit in the multisite system and each group of units. A track mask is also maintained for each user and group in the system. The site masks are static and are stored in a system manager for the system. The site mask must be up-loaded from the system manager to appropriate nodes in the switch when a call is initially placed. The track mask is dynamic and is continuously updated by log-ins and call activity from the units in the various sites.
In the preferred embodiment, each mask is a 16-bit field. Each bit corresponds to a particular site. A one (1) bit signifies that this site should be involved in calls to the group or individual associated with the mask. A group can have multiple bits set in its site and track masks because there may be group members spread over several sites. An individual may have multiple bits set in his site mask but only one bit set in his track mask. An individual can be in only one site at a time. Accordingly, the track mask should only have one bit set at a time. By use of these masks, the multisite switch can determine which sites should participate in a call and which sites have certain units and group members. Using this information, the switch can route audio to the appropriate sites.
The present invention relates to a multisite switch having a distributed architecture. The logical functions of the switch are shared by various microprocessor operated nodes distributed throughout the switch. The nodes share the computational workload of the switch. Each node is connected to a site controller, dispatcher console, the system manager or other component of the overall radio system. The nodes coupled to site controllers are referred to as Master II Interface Modules (MIMs) and the nodes coupled to dispatcher consoles are referred to as Console Interface Modules (CIMs).
Each node of a multisite network switch is supported by a switch controller card operated by microprocessors. All of the cards have substantially the same hardware and are interchangeable. The MIM and CIM cards have identical hardware. There is one card for each site controller and each dispatcher console coupled to the switch. Each card acts as a gateway into the network for its site controller or dispatcher console.
The multisite switch does not completely fail if one network node card breaks down. Wide area communications, i.e. calls between site areas, continue despite the failure of a node. If a card fails, then the gateway to the network is closed only for its site controller or dispatcher console. Failure of a node prevents wide area communications only with respect to the site or console connected to the failed node. Mobile units in the area serviced by the failed card will not be able to call a unit in another area or receive calls from another area.
Local communications within an area are not disabled by the failure in the multi site switch. A site controller is not disabled by a failure of its associated node in the multisite switch. In particular, the failure of a MIM does not disable the site controller to which the MIM is connected. The site controller continues to operate and local communications within the area are unaffected by a failure in the multisite switch.
The ability to continue wide area calls after a node in the switch has failed provides several advantages to a distributed architecture switch over a central architecture switch. In a central architecture, a central processing unit (CPU) governs the operation of the switch. If this CPU fails, then the entire switch fails. Wide area communications are completely shut down by the failure of a multisite switch having a central architecture. As already stated, wide area communications are not completely shut down by a failure in a switch having a distributed architecture.